Protecting layer

ABSTRACT

A protective layer for load-transferring contact surfaces of gas turbine components, especially titanium turbine components is capable to take up alternating loads at higher temperatures. The protective layer is formed of an alloy having the following composition in percent by weight: aluminum (Al) 4-8%; chromium (Cr) 2-5%; iron (Fe) 0-3.5%; and copper (Cu) remainder.

FIELD OF THE INVENTION

The invention concerns a protective layer for load-transferring contactsurfaces of gas turbine components made of alloys based on titanium,nickel, cobalt or iron against friction wear, friction corrosion and/orfriction fatigue.

BACKGROUND INFORMATION

The surfaces of component pairs with positive fit in gas turbine powerplants, especially in the area of rotating blade foot/disk groove, tendto undergo fretting wear, i.e., friction corrosion or friction wear whenoscillating at high frequencies at low amplitudes and at hightemperatures. Temperatures above approximately 450° C. stronglyaccelerate wear. In bad cases, cracks caused by fretting fatigue, i.e.,friction fatigue, can lead to premature failure of the component.

U.S. Pat. No. 5,312,696 (Beers et al.) discloses a protective layeragainst fretting wear for components made of nickel, cobalt or titaniumalloys, which protective layer consists of copper and aluminum, possiblywith silicon as an additional alloy element. The percent by weight ofthese alloy elements lies within the following ranges:

Cu 88-96% Al  4-8% Si  0-4%

Preferred compositions of these aluminum bronzes without added siliconcontain 92% Cu and 8% Al or 92.5% Cu and 7.5% Al. It was shown thatlayers According to this U.S. Patent possess sufficient high-temperatureoxidation resistance, however their heat resistance drops drasticallyabove 450° C. The surface pressure at the blade foot/disc groove eatsaway such layers from the contact zone and causes them to fail (cakedough effect).

German Patent 42 29 600 C1 (Grunke et al.) concerns a layer structurefor titanium components with a metal intermediate layer and outerprotective layer. The latter is formed by a copper/aluminum alloy orother alloys, preferably with a composition of CuAl₈. Apart from theadditionally requited intermediate layer, the same considerations applyto the cover layer of aluminum bronze as discussed above with referenceto the U.S. Patent. The other alloys for alternative protective/coverlayers are not bronzes, i.e. not copper alloys, and will therefore notbe further discussed in this context.

SUMMARY OF THE INVENTION

In view of the above prior art protective layers and theirdisadvantages, the problem of the invention is to present a protectivelayer based on a copper/aluminum alloy for load-transferring contactsurfaces of components, especially titanium components that stronglyresist oxidation, corrosion and friction wear, especially attemperatures above 450° C., that is therefore particularly useful in gasturbine drives.

This problem is solved by the present protective layer formed by analloy that contains copper as the main element and aluminum and chromiumas additional elements. Iron as an additional element can furtherimprove the protective properties. The element chromium (Cr) with 2-5%parts by weight particularly increases the heat resistance and thehigh-temperature oxidation resistance while simultaneously leaving theprotective layer sufficiently ductile. More specifically, according tothe invention there is provided a gas turbine component for operation attemperatures above at least 450° C., said gas turbine componentcomprising a base structure made of alloys made of alloying elementsselected from the group consisting of titanium, nickel, cobalt and iron,said base structure comprising a contact surface for cooperation withother turbine components, said gas turbine component further comprisinga protecting layer on said contact surface for protection againstfretting, wherein said protecting layer is made of an alloy consistingof aluminum 4 to 8% by wt., chromium 2 to 5% by wt., iron 0 to 3.5% bywt., the remainder being copper plus unavoidable impurities.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BESTMODE OF THE INVENTION

The preferred chromium content in the above example is 3% by weight.

A range of 20-50 μm is advantageous for the layer thickness.

It is convenient to deposit the protective layer by physical vapordeposition (PVD). The method of cathode sputtering is preferred. In thismethod, a cathode consisting of the protective layer alloy is removed bythe sputter effect in a glow discharge, and the arising metal vapor isdeposited on the component, e.g. a compressor rotor blade of a gasturbine.

The protective layer according to the invention has proven itself wellin experiments.

Although the invention has been described with reference to specificexample embodiments, it will be appreciated that it is intended to coverall modifications and equivalents within the scope of the appendedclaims. It should also be understood that the present disclosureincludes all possible combinations of any individual features recited inany of the appended claims.

What is claimed is:
 1. A gas turbine component for operation attemperatures above at least 450° C., said gas turbine componentcomprising an alloy base structure made of alloying elements selectedfrom the group consisting of titanium, nickel, cobalt and iron, saidalloy base structure comprising a contact surface for cooperation withother turbine components, said gas turbine component further comprisinga protecting layer on said contact surface for protection againstfretting, wherein said protecting layer is made of an alloy consistingof aluminum 4 to 8% by wt., chromium 2 to 5% by wt., iron 0 to 3.5% bywt., the remainder being copper plus unavoidable impurities.
 2. The gasturbine component of claim 1, wherein said chromium is present at 3% bywt.
 3. The gas turbine component of claim 1, wherein said protectinglayer has a thickness within the range of 20 to 50 μm.
 4. The gasturbine component of claim 1, wherein said protecting layer is aphysical vapor deposition layer.
 5. The gas turbine component of claim4, wherein said protecting layer is a cathode sputtering layer.